1. Filed of the Invention
The present invention relates to a wafer heating apparatus used to treat and heat a wafer placed thereon, particularly in filmmaking or etching on a wafer in processes of semiconductor devices.
In filmmaking apparatuses such as plasma CVD, low pressure CVD, optical CVD or PVD systems, or in etching apparatuses based on plasma etching or optical etching technique in the production step of semiconductor devices.
2. Prior Art
wafer heating apparatuses have been used to treat wafers in filmmaking systems such as plasma CVD, low pressure CVD, optical CVD or PVD systems, or in etching systems based on plasma etching or optical etching technique, particularly, for production of semiconductor devices.
In the filmmaking systems, corrosive gases, such as chlorine and fluorine gases, have been used as a deposition gas, an etching gas and a cleaning gas in the plasma CVD system, or other depositing and etching systems in the processes for producing semiconductor devices.
As wafer heating apparatus for holding a wafer, including a semiconductor wafer (hereinafter referred to as "wafer"), in such an atmosphere of the above gas and heating the wafer to a process temperature, a stainless heater incorporating a heating resistor therein has been used.
However, the stainless heater has the problem that the heater is apt to be corroded while being exposed to the above corrosive gases, which results in producing particles to be separated from the wafer holder.
On the other hand, a method has been adopted in which a wafer heating apparatus have been made of graphite, which has relatively high corrosion resistance to such corrosive gases, and have been indirectly heated by infrared lamps outside a chamber. But this had a drawback of lower heat efficiency compared to direct heating process. Moreover the method also has the problem that for a filmmaking system a film deposits on the surface interior wall of the chamber, and a great deal of light form the lamps is absorbed in the film attached on the window glass for the lamps, thus making the wafer heating apparatus unable to heat.
As a wafer heating apparatus which eliminates the problems described above, Japanese Patent Publication JP-A 6-52974 discloses a wafer heating apparatus 11 in which the top surface of a dense ceramic substrate 12 of disk shape as shown in FIG. 9, is used as a supporting surface 13 for a wafer W, and a heating wire resistor 14 formed of a metal having a high melting point and a planular-section is buried in the disk ceramic substrate. The heating resistor 14 buried in the apparatus 11 is provided in a spiral configuration in the area if the disk ceramics as a heater pattern, as shown in FIG. 10.
However, the wafer heating apparatus 11 has a problem that the spiral heating wire resistor is difficult to uniformly heat the wafer W placed on the supporting surface 13. In the other words, with the heating resistor made in the spiral configuration, the planular-section wire heating resistor 14 is interrupted at one end thereof in the periphery of the ceramic substrate 12, thus causing poor uniformity of heating in the periphery of the wafer heating apparatus 11, resulting in significant unevenness in heating of the supporting surface 13 as a whole, thus failing to heat the wafer W uniformly.
Consequently, when a film is formed by using the wafer heating apparatus 11, the film cannot be formed with a uniform thickness on the water W and, in the case of etching process, there have been such problems as significant variations in the processing accuracy, resulting in poor product yield.